1. Field of the Invention
The present invention relates to an autofocus lens barrel using a belt as a means of driving an autofocus lens.
2. Related Background Art
FIG. 3 is a cross-sectional view showing an example of a conventional autofocus lens barrel. In FIG. 3, a reference numeral 101 designates a lens mount; 102, a fixed barrel fixed to the lens mount 101; 103, a rotational barrel rotatively fitted along the internal periphery of the fixed barrel 102 with the optical axis as its center, and on the inner periphery of the rotational barrel 103, a helicoid 103b is formed while on the outer periphery of the lens mount 101, a segment gear 103a is formed. A reference numeral 104 designates a holding barrel having a helicoid 104a on the outer periphery thereof to engage with the helicoid 103b, at the same time, holding an optical system 110 with its inner periphery, and 114, a coupling shaft with a pinion gear 114a on the outer periphery thereof to engage with the segment gear 103a.
Subsequently, the description will be made of the operation of an autofocus lens barrel shown in FIG. 3. The driving force from a camera body (not shown) is transmitted to a coupling shaft (concave side) 114 provided for the mount 101 on the lens side through the coupling shaft (convex side, not shown) which is arranged on the mounting plane (not shown) on the body side. The driving force transmitted to the coupling shaft (concave side) 114 is transmitted to a rotational barrel 103 as a rotational motion through a pinion gear 114a formed on the coupling shaft (concave side) 114 and the segment gear 103a. Accompanying this, the holding barrel 104 which holds a focusing optical system 110 is driven in the direction of the optical axis by the function of the helicoid 103b and helicoid 104a.
However, in the conventional autofocus lens barrel which has been described above, a problem is encountered in that the lens barrel using the gear driving makes driving sounds when gears are driven in a site of photographing where people tend to be nervous about any sounds.
Also, there is a problem that due to reactive force given to the sliding portion of the rotational barrel to be driven, efficiency is lowered, and that due to such a lowered efficiency, an uneven operation results from the difference in the positions of the lens barrel, or there is a disadvantage that hunting is generated.